On hypoellipticity for a class of pseudo-differential operators
On hypoellipticity for a class of pseudo-differential operators
Introduction and ResultsWe shall study hypoellipticity for a class of pseudo-differential operators which includes the operator $-a(x)\Delta+1$ with $a(x)\geq 0$ as a typical example.We shall use the Weyl symbols and the Weyl calculus in this paper.For the Weyl calculus we refer to Hormander [2].Let $p(x, \xi)\in S^{m}(\equiv S_{1}^{m_{0}}(R^{2n}))$ , i.e., …